Based on your explanation, an equivalent idiom in English would be (to) pass the buck:
To transfer responsibility or blame from oneself onto another; to absolve oneself of concern for a given matter by claiming to lack authority or jurisdiction.
The phrase also comes with its own Wikipedia page.
The two earliest instances I can find for OP's exact sense are...
1911 What say we play house with your'n, and we take mine home to yer maw so she won't jaw?
1914 What say we haze them sheep a few miles north, boys?
It's probably relevant to note that both cases involve a significantly "non-standard" speaker.
As noted, the "What say you?" dating back to Shakespeare isn't precisely the same usage, because it refers back to a question or issue previously raised (effectively, "What say you to that?"), whereas OP's usage refers forward to a suggestion about to be raised by the rest of the sentence.
I think it's particularly a characteristic of informal/careless/uneducated speech to discard quite a lot of words if they contribute little to the sense of an utterance (either because they're highly predictable, or because they're only there for the sake of grammaticality. The less well-educated hostess might be more likely to say "Cuppa?" where Lady Muck says "Would you like a cup of tea?"
Here's an earlier instance of an expanded form in Jack London's 1903 Novels and Social Writings...
What do you say we all go out and have a drink on it?
I see the modern usage as just a contracted form of "What do you say to the proposal that we...?" which doesn't actually adhere to any grammatical rules at all. By contrast, "What say you?" was perfectly grammatical in Shakespeare's day (before do-support rose to prominence, and we started replacing constructions like "Know you him?" with "Do you know him?").
Best Answer
The phrasal verb stop by is generally used to mean “to visit someone briefly.” It seems you want to use it to mean a “short visit.” I would advise the following: If you say where you’re stopping by (i.e. the coffee shop), then you can fulfill the word’s definition. In other words, saying “I stopped by the coffee shop to get some coffee” would correlate with the definition “to visit someone briefly.” Even though you aren’t visiting someone per se, you are visiting something (a coffee shop). The main definition is, after all, “to visit [someone or something] briefly.” Truthfully, you can put anything in the brackets; the main idea is “to visit briefly.”
Also, if you leave out where you stopped by, it becomes ambiguous: Where did you stop by to get coffee? At your neighbor’s house? At the store? Saying where you stopped by removes any ambiguity.
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